This invention relates generally to the field of wind energy conversion systems and, more particularly, to an improved diffuser for augmenting a wind turbine.
A diffuser is a passage so shaped (usually in the form of a divergent duct) that it will change the characteristics of a fluid flow from a certain pressure and velocity at the inlet to a lower velocity and higher pressure at the outlet. Generally, the diffusion must be carried out in a well-streamlined passage having smooth interior surfaces, and sides not diverging at so great an angle as to cause the fluid to leave the sides of the diffuser. By reducing the velocity through increasing the cross-sectional area of flow, the pressure may be built up as the velocity head is diminished. Diffusers are used to conserve energy by efficiently converting velocity head into pressure.
Thus the power generating capability of a conventional wind turbine can be increased by installing it at the entrance of a diffuser.
In all energy conversion systems, cost and efficiency are paramount considerations. Early investigations of diffuser augmentation were discouraging because it was believed that diffuser efficiency could only be achieved by the use of a small included angle, implying a long and costly diffuser. Recent advances in diffuser augmentation have relied upon the principle of boundary layer control to permit the use of a shorter length, wide angle diffuser. An example of a diffuser augmented wind turbine using various structures to energize the boundary layer and prevent flow separation from the diffuser walls (the major cause of inefficiency in short, wide angle diffusers) is shown in Oman et al U.S. Pat. No. 4,075,500.
In addition to the aforementioned aerodynamic problems with diffuser augmented wind turbines, there are also important structural considerations. Commercially feasible wind turbines have rotors of the order of 100 feet in diameter and this necessitates a diffuser of comparable size for augmentation. Large diffusers require more material to maintain structural rigidity, adding to the overall weight, and more supports to withstand wind forces impinging on the diffuser. Consequently, effective as boundary layer control devices have been, there is still a need to reduce diffuser length and increase power efficiency (thereby reducing costs) even more.
Therefore, it is an object of the present invention to provide an improved diffuser for augmenting a wind turbine with significantly reduced axial length.
It is also an object of the present invention to provide an improved diffuser that increases power output of a conventional wind turbine.
It is another object of the present invention to provide a diffuser with improved structural rigidity and stability.
Other objects and advantages will become apparent from the description set forth hereafter.